The present invention relates to a silicone resin and a process for producing a silicone resin, which resin is composed solely of difunctional siloxy units and more specifically, the present invention relates to silicone resins composed solely of difunctional siloxy units which can be mixed with other silicone resins to produce a silicone resin mixture with optimum thermal stability properties.
Silicone resins having good thermal stability are well-known, for instance see the disclosure in Merrill patent application, Ser. No. 628,001, entitled Fast Curing Silanol-Containing Organopolysiloxane Resins and a Method for Making Them.
Most of such silicone resins are stable only at temperatures as high as 600.degree. F. At the 700.degree. F temperature level such resins are rarely thermally stable for prolonged periods of time. Accordingly, it is highly desirable to produce a silicone resin or a silicone resin mixture which would have as high a thermal stability as possible and specifically have a good thermal stability at 700.degree. F.
As pointed out previously, standard silicone resins were only occasionally thermally stable at such high temperatures as 700.degree. F for any measurable period of time. It should also be pointed out, that it was desirable that silicone resins be thermally stable, that is, that they would not crack or craze at temperatures as high as 700.degree. F or above since such silicone resins are preferred ingredients for producing electrical junction coatings, electrical encapsulating compositions, silicone paints which are to be utilized to coat electrical components and for producing electrical varnishes.
In a different vein, all silicone resins that have been produced up to the present time have been composed solely of trifunctional siloxy units or of trifunctional siloxy units and difunctional siloxy units, that is they were produced by the hydrolysis of monoorganotrichlorosilane and diorganodichlorosilane to produce a silicone resin where the organo to Si ratio may vary anywhere from 1.1 to 1.9:1.
As pointed out above it has also been possible up to the present time to produce silicone resins composed solely of trifunctional siloxy units and such silicone resins are highly desirable in many applications, including the encapsulation of electrical components. However, most silicone resins were formulated with a certain amount of difunctional siloxy units in them, since silicone resins composed solely of trifunctional siloxy units are very brittle. Accordingly, the difficulty with such solely trifunctional silicone resins or silicone resins which had no difunctional siloxy units in them was that such resins tended to be brittle and as such would shatter upon being struck a sharp blow by some object.
Accordingly, silicone resins for most applications were formulated with a certain amount of difunctional siloxy units in them by hydrolyzing a mixture of the appropriate amount of trihalosilanes with dihalosilanes so as to obtain the desired organo to Si ratio desired in the final silicone resin product.
However, such formulations created certain problems with respect to formulators of silicone resins which utilize silicone resins to produce other products, such as silicone paints. Thus, such formulators or producers of silicone paints would obtain a silicone resin from a silicone manufacturer having a certain organo to Si ratio and the formulators would attempt to formulate a silicone paint having a certain rigidity and flexibility in it.
It can be appreciated, as stated above that the formulator was restricted in his freedom in formulating his particular composition since the properties of the silicone resin sold to him by the silicone manufacturer were fixed and specifically the organo group to Si ratio in the resin was fixed. All the formulator could do previously would be to specify a silicone resin for his use with a certain organo group to Si ratio. Once he had received the resin from the manufacturer he could not change this ratio.
Accordingly, it was highly desirable to obtain a silicone resin composed solely of difunctional siloxy units. That is a true silicone resin and not a fluid which silicone fluids have been produced by previous processes that attempted to produce an all difunctional silicone resin. Accordingly, a formulator of silicone paints, electrical varnishes, and electrical encapsulating compositions, junction coatings and what not, if he had an all difunctional silicone resin, he could take one of the standard silicone resin products that are currently on the market and by adding the appropriate amounts of the solely difunctional silicone resin to the standard products could formulate a silicone resin mixture that had the optimum properties for his particular application.
It can be appreciated that the addition of an all difunctional silicone resin to a standard silicone resin product would be highly desirable if such addition would not take away from the thermal stability of the standard product silicone resin, and if such silicone resin would be compatible with such standard silicone resin product and would impart to such standard silicone resin product the desired amount of plasticity that is desired for a silicone resin varnish or paint.
Accordingly, it is one object of the present invention to provide for an all difunctional silicone resin and a process for producing an all difunctional silicone resin.
It is another object of the present invention to provide for an all difunctional silicone resin with good thermal stability.
It is an additional object of the present invention to provide for a silicone resin mixture and a process for forming a silicone resin mixture, which mixture is composed of an all difunctional silicone resin and a silicone resin composed of trifunctional siloxy units and difunctional siloxy units where the resulting silicone resin mixture has good thermal stability at excessively high temperatures.
These and other objects of the present invention are accomplished by means of the disclosure set herein below.